Bond capillary design for ribbon wire bonding

ABSTRACT

A device ( 100 ) and method ( 200 ) for bonding a ribbon wire ( 104 ) to a workpiece ( 106 ) comprising feeding the ribbon wire through a passageway ( 116 ) of an ultrasonic bond capillary ( 102 ) and clamping the ribbon wire against an engagement surface ( 120 ) of the bond capillary via a clamping jaw ( 118 ) operably coupled to the bond capillary. The ribbon wire ( 104 ) is bonded to the workpiece ( 106 ) along a bonding surface ( 112 ) of the bond capillary ( 102 ) and penetrated, at least partially, between the bonding surface and the engagement surface ( 120 ) of the bond capillary by a cutting tool ( 124 ). The cutting tool ( 124 ) may comprise an elongate member ( 126 ) positioned between the bonding surface ( 112 ) and engagement surface ( 120 ), and may have a cutting blade ( 128 ) positioned at a distal end ( 130 ) thereof. The cutting tool ( 124 ) may further comprise a ring cutter ( 132 ), wherein the ribbon wire passes through a ring ( 134 ) having a cutting surface ( 138 ) defined about an inner diameter thereof.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a division of Ser. No. 11/148,687, filed Jun. 9,2005, now U.S. Pat. No. 7,216,794 the contents of which are hereinincorporated by referenced in its entirety.

FIELD OF THE INVENTION

The present invention relates generally to semiconductor devices andprocesses, and more particularly to device and method for bonding aribbon wire to a workpiece.

BACKGROUND OF THE INVENTION

In the semiconductor industry, wire bonding is commonly performed toelectrically interconnect an integrated circuit (IC), such as asemiconductor die or chip, to various structures, such as a metalleadframe. Wedge bonding, for example, is a conventional method used tobond thin wires, such as thin aluminum or gold wire, between a bondingpoint on the semiconductor die to another point, such as a lead fingerof the leadframe. Conventionally, in order to initiate a bond, the wireis pressed against the IC and/or leadframe with a tip of a bonding tool.The bonding tool is ultrasonically vibrated for a period of tens ofmilliseconds, wherein a plane of motion of the tip of the bonding toolis generally parallel to the surface of the semiconductor chip to whichthe bond is to be formed. The combination of a static load of thebonding tool normal to the chip's surface against the wire and chipcoupled with the vibration at the tip of the tool causes the wire toplastically deform, thus simultaneously joining the bond wire with atomsof the material composing the chip's or leadframe's surface, andaccordingly, providing a cold weld between the wire and the chip orleadframe.

One problem associated with wire bonding is the handling of the wirethroughout the bonding process, and the breaking or severing of the wireafter the bond has been made. To perform these functions, mostconventional fine wire wedge bonding tools break the wire by clampingand/or pulling the wire away from the bonded substrate. Typically, withsmall diameter wires (circular cross-section wires having diameters ofless than 0.025 inches), such a pulling action is sufficient, and doesnot cause significant damage to the substrate. However, with theever-increasing demands for speed and performance of ICs, ribbon wireshave been introduced, wherein a cross-sectional area of the ribbon wiresis significantly greater than previously-used round cross-section wires,thus providing greater electrical current-carrying capabilities for thewire. Accordingly, when the conventional bonding tools are used with thethicker ribbon wires, the pulling force required to break the ribbonwire tends to deleteriously deform the chip and/or leadframe. As aconsequence, various configurations for bonding tools have beenformulated, such as one wherein a blade is pressed against the chipand/or leadframe in order to deform or cut the ribbon wire prior topulling the bonding tool away from the substrate.

FIGS. 1A-1C illustrate one such conventional bonding device 10 duringvarious operations, wherein a ribbon wire 15 is bonded to a substrate20, such as a leadframe finger or semiconductor chip by an ultrasonicbonding tool 25. As illustrated in FIG. 1A, the bonding tool 25 ispressed against the ribbon wire 15, thus compressing the ribbon wirebetween the bonding tool and the substrate 20. At this point, thebonding tool 25 ultrasonically vibrates, thus cold-welding the ribbonwire 15 to the substrate 20. FIG. 1B illustrates a cutter 30 that ispressed against the ribbon wire 15, wherein the cutter significantlythins or cuts through the ribbon wire by the force F exerted by thecutter. FIG. 1C illustrates the bonding tool 25 being pulled away fromthe substrate 20, wherein a clamp 35 further pulls the ribbon wire 15from the substrate, thus fully severing the ribbon wire generally at atip 40 of the cutter 30.

One problem with the conventional bonding of ribbon wires, however, isthat the force F of the cutter 30 against the ribbon wire 15 illustratedin FIG. 1B typically translates into a force on the substrate 20,wherein the substrate is potentially permanently deforming and/ordamaged by the cutting operation. For example, as in the case of theribbon wire 15 being bonded to a thin leadframe finger, the force Fsignificantly deforms the leadframe finger (as illustrated by arrow 45),wherein the deformation remains after the cutter is pulled away from thesubstrate 20. Furthermore, if the ribbon wire 15 is not completelysevered, the pulling force may further bend the leadframe finger in adirection opposite of the arrow 45 when the clamp 35 pulls the ribbonwire away. Alternatively, as in the case of the ribbon wire 15 beingbonded to a chip, the cutting force F can deleteriously impact the chip,such as potentially damaging metallization layers or other layers of theIC.

Therefore, a need currently exists for a reliable process and apparatusfor bonding ribbon wires to substrates, wherein damage to the substrateis substantially minimized.

SUMMARY OF THE INVENTION

The present invention overcomes the limitations of the prior art byproviding an improved device and method for bonding wires to varioussubstrates. Accordingly, the following presents a simplified summary ofthe invention in order to provide a basic understanding of some aspectsof the invention. This summary is not an extensive overview of theinvention. It is intended to neither identify key or critical elementsof the invention nor delineate the scope of the invention. Its purposeis to present some concepts of the invention in a simplified form as aprelude to the more detailed description that is presented later.

The present invention is generally directed toward an improved deviceand method for bonding a ribbon wire to a workpiece. According to oneexemplary aspect of the invention, the device comprises an ultrasonicbond capillary having a body region and a bonding region, wherein thebody region comprises a passageway defined therein. The ribbon wiregenerally extends through the passageway and along a bonding surfaceassociated with the bonding region, and a clamping jaw is operablycoupled to the ultrasonic bond capillary in the vicinity of thepassageway. Accordingly, the clamping jaw is operable to selectivelygrip the ribbon wire between an engagement surface of the passageway anda clamping surface of the clamping jaw.

A cutting tool is further operably coupled to the ultrasonic bondcapillary and generally positioned between the bonding surface and theengagement surface of the bond capillary. The cutting tool, for example,is operable to selectively extend and retract with respect to theultrasonic bond capillary, wherein the cutting tool can at leastpartially penetrate through the ribbon wire positioned between thebonding surface and engagement surface of the ultrasonic bond capillary.Such a penetration of the ribbon wire between the bonding surface andthe engagement surface while the ribbon wire is substantially clampedwith respect to the bond capillary is highly advantageous over the priorart, since the cutting action of the cutting tool does not press on theworkpiece, but rather, cuts the ribbon wire between two generally fixedand/or clamped regions.

In accordance with another exemplary aspect of the invention, one ormore of the clamping jaw and cutting tool are operably coupled to thebond capillary by one or more actuators, such as electromechanicalactuators. The electromechanical actuators may comprise one or more of aservo motor, linear motor, spring actuator, pneumatic, and hydraulicactuators operable to selectively extend and retract the respectiveclamping jaw and cutting tool with respect to the ultrasonic bondcapillary. The cutting actuator, for example, may comprise a springoperable to extend the cutting tool with respect to the ultrasonic bondcapillary, while a magnetic or electromagnetic actuator retracts thecutting tool, or vice-versa.

According to another example, the cutting tool comprises an elongatemember having a cutter blade generally defined at a distal end thereof.The cutting tool may further comprise a ring cutter having an innerregion defined at the distal end of the elongate member, wherein theribbon wire generally passes through the inner region of the ring, andwherein the cutting blade is generally defined by a cutting surfaceabout an inner diameter of the ring. The ring cutter is then operable toselectively penetrate or sever the ribbon wire upon retraction of thecutter ring toward the bond capillary.

To the accomplishment of the foregoing and related ends, the inventioncomprises the features hereinafter fully described and particularlypointed out in the claims. The following description and the annexeddrawings set forth in detail certain illustrative embodiments of theinvention. These embodiments are indicative, however, of a few of thevarious ways in which the principles of the invention may be employed.Other objects, advantages and novel features of the invention willbecome apparent from the following detailed description of the inventionwhen considered in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1C illustrate a conventional bonding device in variouspositions during bonding.

FIG. 2 illustrates a partial cross-sectional view of an exemplarybonding device according to one aspect of the present invention.

FIG. 3 illustrates a plan view of a ring cutter according to anotherexemplary aspect of the present invention.

FIG. 4 is a block diagram schematic of an exemplary method for bonding aribbon wire to a workpiece in accordance with the present invention.

FIGS. 5A-5F illustrate partial cross-sectional views of an exemplarybonding device during various operations in accordance with anotheraspect of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed towards an apparatus and method forbonding a wire to substrate or workpiece, such as an integrated circuit(IC) and/or leadframe assembly. More particularly, the present inventionprovides a robust and reliable device and process for bonding arectangular cross-section ribbon wire to the substrate, wherein damagesor deformations to the substrate seen in conventional bondingapparatuses and processes are substantially mitigated. Accordingly, thepresent invention will now be described with reference to the drawings,wherein like reference numerals are used to refer to like elementsthroughout. It should be understood that the description of theseaspects are merely illustrative and that they should not be taken in alimiting sense. In the following description, for purposes ofexplanation, numerous specific details are set forth in order to providea thorough understanding of the present invention. It will be evident toone skilled in the art, however, that the present invention may bepracticed without these specific details.

Referring now to the figures, FIG. 2 illustrates a partialcross-sectional view of an exemplary bonding device 100, wherein one ormore exemplary aspects of the present invention will now be discussed.The bonding device 100, in accordance with one exemplary aspect of thepresent invention, comprises an ultrasonic bond capillary 102 forultrasonically bonding a ribbon wire 104 to a substrate or workpiece106, such as one or more of an IC chip or a leadframe. The ultrasonicbond capillary 102, for example, is operably coupled to an ultrasonicoscillator (not shown), as is known in the art for providing anultrasonic vibration to the bond capillary. The ultrasonic bondcapillary 102 comprises a body region 108 and a bonding region 110,wherein the ultrasonic bond capillary is operable to sandwich the ribbonwire 104 between a bonding surface 112 of the ultrasonic bond capillaryand a surface 114 of the workpiece 106. The body region 108 of the bondcapillary 102, for example, comprises a passageway 116 defined therein,wherein the ribbon wire 104 further generally extends through thepassageway and along the bonding surface 114 associated with the bondingregion 110. The passageway 116 may be comprised of a thru-hole, achannel, or various other surfaces (not shown) defined within or alongthe body region 108, wherein the ribbon wire 104 is operable to extendalong the passageway. In one example, the ribbon wire 104 is generallyrectangular in cross-section, wherein the passageway is also generallyrectangular in cross-section.

FIG. 2 further illustrates a clamping jaw 118 operably coupled to thebond capillary 102 in the body region 110 thereof, wherein the clampingjaw is further associated with the passageway 116. The clamping jaw 118is operable to selectively grip the ribbon wire 104 between anengagement surface 120 of the passageway 116 of the bond capillary 102and a clamping surface 122 of the clamping jaw 118. In the presentexample, the engagement surface 120 of passageway 116 is generallyplanar, wherein the passageway is generally defined between the bodyregion 110 of the bond capillary 102 and the clamping surface 122 of theclamping jaw 118. Alternatively, the passageway 116 may be defined by achannel (not shown) or other structure associated with the body region110 of the bond capillary 102, wherein the clamping jaw 118 is operableto substantially grip or prevent movement of the ribbon wire 104 withinthe passageway.

The clamping jaw 118 of the present invention may be operably coupled toan electro-mechanical actuator (not shown), wherein theelectro-mechanical actuator is operable to retract and/or extend theclamping jaw, thus respectively gripping and/or releasing the ribbonwire 104. For example, the clamping jaw 118 may be operably coupled to amotor (not shown), such as a servo motor, wherein the motor is operableto selectively extend and retract the clamping jaw with respect to theengagement surface 120. The clamping jaw 118 may be further coupled toone or more springs (not shown), wherein the one or more springs arefurther operable to substantially extend or retract the clamping jawwith respect to the engagement surface 120. Alternatively, the clampingjaw 118 may be operably coupled to a pneumatic or hydraulic actuator(not shown), wherein the pneumatic or hydraulic actuator is operable toextend and retract the clamping jaw with respect to the engagementsurface 120. Accordingly, any actuator operable to extend and/or retractthe clamping jaw 118 with respect to the engagement surface 120 of thebond capillary 102 is contemplated as falling within the scope of thepresent invention. It should also be noted that the clamping jaw isgenerally integrated with the bond capillary 102, wherein the engagementsurface 120 of the bond capillary 102 is generally near the bondingsurface 114, as will be discussed hereafter.

According to another exemplary aspect of the present invention, thebonding device 100 further comprises a cutting tool 124, wherein thecutting tool is further operably coupled to the bond capillary 102. Thecutting tool 124, for example, is generally positioned between thebonding surface 114 and the engagement surface 120 of the bond capillary102, wherein the cutting tool is operable to selectively extend andretract with respect to the bond capillary. The cutting tool 124, forexample, comprises an elongate member 126, wherein a cutting blade 128is generally defined at a distal end 130 thereof. The cutting blade 128,for example, may be flattened, as illustrated in FIG. 2, or mayalternatively converge to a point (not shown) at the distal end 130 ofthe cutting tool. According to the invention, the cutting tool 124 isoperable to penetrate, at least partially, through the ribbon wire 104between the bonding surface 114 and engagement surface 120 of theultrasonic bond capillary 102 when the cutting blade 128 is extendedpast the clamping surface 122 of the clamping jaw 118 in a shear-likemanner.

In another example, the cutting tool 124 comprises a ring cutter 132, asillustrated in FIG. 3. The ring cutter 132, for example, comprises aring 134 positioned at the distal end 130 of the cutting tool 124 ofFIG. 2, wherein the ribbon wire 104 generally passes through an innerregion 136 of the ring. The ring cutter 132 of FIG. 3 is operable toselectively extend and retract in a manner similar to the cutting blade128 of FIG. 2, however, a cutting surface 138 of the ring cutter isoperable to generally pass through the ribbon wire when being retractedtowards the body region 110 of the bond capillary 102. Accordingly, thering cutter of FIG. 3 is operable to be drawn against the engagementsurface 120 of the bond capillary, thus penetrating, at least partially,through the ribbon wire 104.

In accordance with another exemplary aspect of the invention, thecutting tool 124 of FIG. 2 is operably coupled to a cutting actuator(not shown), such as an electro-mechanical actuator, servo motor, orother actuator, such as those described in reference to the clamping jaw118. The cutting tool 124, for example, may be coupled to a magneticactuator (not shown) and a spring (not shown), wherein the magneticactuator is operable to retract the cutting tool (e.g., pull the distalend 130 of the cutting tool toward the body region 108 of the bondcapillary 102), and wherein the spring is operable to provide a returnforce to the cutting tool, thus extending or returning the distal end ofthe cutting tool to its original position.

According to another aspect of the present invention, FIG. 4 is a blockdiagram illustrating an exemplary method 200 for bonding a ribbon wireto a substrate. While exemplary methods are illustrated and describedherein as a series of acts or events, it will be appreciated that thepresent invention is not limited by the illustrated ordering of suchacts or events, as some steps may occur in different orders and/orconcurrently with other steps apart from that shown and describedherein, in accordance with the invention. In addition, not allillustrated steps may be required to implement a methodology inaccordance with the present invention. Moreover, it will be appreciatedthat the methods may be implemented in association with the systemsillustrated and described herein as well as in association with othersystems not illustrated.

The method 200 of FIG. 4 will now be described with reference to FIGS.5A-5F, in order to gain a more complete understanding of the presentinvention. As illustrated in FIG. 4, the method 200 begins with act 205,wherein a ribbon wire is fed through a bond capillary. As illustrated inFIG. 5A, the ribbon wire 104 is fed through the passageway 116 of thebond capillary 102 when the clamping jaw 118 is generally extended, thusgenerally permitting the advancement of the ribbon wire through thepassageway. In act 210 of FIG. 4, the ribbon wire is clamped against thebond capillary, and the result of act 210 is illustrated in FIG. 5B. Forexample, the clamping jaw 118 generally sandwiches the ribbon wire 104between the clamping surface 122 of the clamping jaw and the engagementsurface 120 of the bond capillary 102.

In act 215 of FIG. 4, the ribbon wire is bonded to the workpiece, suchas by a cold welding the ribbon wire 104 of FIG. 5B to the workpiece 106by ultrasonic vibration of the bond capillary 102. In one example, oncethe ribbon wire 104 is generally bonded to the workpiece 106, the ribbonwire can be cut by the cutting tool 124 in act 220 of FIG. 4. FIGS.5C-5D illustrate the cutting tool 124 extending from the body region 108of the bond capillary 102, wherein in FIG. 5D, the cutting tool 124completely severs the ribbon wire 104. It should be noted that the ringcutter 132 of FIG. 3 may be alternatively utilized, wherein the ringcutter is retracted toward the bond capillary to cut the ribbon wire 104of FIGS. 5A-5F. Once the cutting tool 124 at least partially penetratesthrough the ribbon wire 104 (illustrated as severing the ribbon wire inFIG. 5D), the bonding tool 100 can be lifted from the workpiece 106, asillustrated in FIG. 5E, thus providing a secure bond 140 of the ribbonwire to the workpiece without damaging, bending, or otherwisedeleteriously affecting the workpiece, as illustrated in FIG. 5F.

Therefore, the present invention provides a device and method forbonding a ribbon wire to a workpiece, wherein the cutting or severing ofthe ribbon wire is performed in a manner that does not significantlydeform the workpiece. By providing a cutting tool and clamping jaw thatare substantially integrated with the bond capillary, no additionalclamping or holding of the ribbon wire or workpiece are required, andthe bonding and cutting of the ribbon wire can be performed withoutbending leadframe fingers or damaging surfaces of the IC chips.Furthermore, the present invention provides a bonding device that can beeasily rotated between bonding positions, thus providing an efficientand reliable bonding of a ribbon wire between the bonding positions.

Although the invention has been shown and described with respect to acertain aspect or various aspects, it is obvious that equivalentalterations and modifications will occur to others skilled in the artupon the reading and understanding of this specification and the annexeddrawings. In particular regard to the various functions performed by theabove described components (assemblies, devices, circuits, etc.), theterms (including a reference to a “means”) used to describe suchcomponents are intended to correspond, unless otherwise indicated, toany component which performs the specified function of the describedcomponent (i.e., that is functionally equivalent), even though notstructurally equivalent to the disclosed structure which performs thefunction in the herein illustrated exemplary embodiments of theinvention. In addition, while a particular feature of the invention mayhave been disclosed with respect to only one of several aspects of theinvention, such feature may be combined with one or more other featuresof the other aspects as may be desired and advantageous for any given orparticular application. Furthermore, to the extent that the term“includes” is used in either the detailed description or the claims,such term is intended to be inclusive in a manner similar to the term“comprising.”

1. A device for bonding a ribbon wire to a workpiece, the devicecomprising: an ultrasonic bond capillary comprising a body region and abonding region, wherein the body region comprises a passageway definedtherein, wherein the ribbon wire extends through the passageway andalong a bonding surface associated with the bonding region; a clampingjaw operably coupled to the ultrasonic bond capillary and associatedwith the passageway, wherein the clamping jaw is operable to selectivelygrip the ribbon wire between an engagement surface of the passageway anda clamping surface of the clamping jaw; and a cutting tool operablycoupled to the ultrasonic bond capillary and positioned between thebonding surface and the engagement surface, wherein the cutting tool isoperable to selectively extend and retract with respect to theultrasonic bond capillary, therein at least partially penetratingthrough the ribbon wire between the bonding surface and engagementsurface of the ultrasonic bond capillary.
 2. The device of claim 1,wherein the ribbon wire has a rectangular cross section, and wherein thepassageway has a rectangular cross section.
 3. The device of claim 1,wherein the clamping jaw is operably coupled to a clamping actuatoroperable to selectively extend and retract the clamping jaw with respectto the ultrasonic bond capillary.
 4. The device of claim 3, wherein theclamping actuator comprises a servo motor operably coupled to theclamping jaw.
 5. The device of claim 1, wherein the ultrasonic bondcapillary is coupled to an ultrasonic oscillator.
 6. The device of claim1, wherein cutting tool is operably coupled to a cutting actuatoroperable to selectively extend and retract the cutting tool with respectto the ultrasonic bond capillary.
 7. The device of claim 6, wherein thecutting actuator comprises a servo motor coupled thereto, wherein theservo motor is operable to selectively extend and retract the cuttingblade.
 8. The device of claim 6, wherein the cutting actuator comprisesa spring operable to extend or retract the cutting tool with respect tothe ultrasonic bond capillary.
 9. The device of claim 1, wherein thecutting tool comprises an elongate member having a cutter blade definedat a distal end thereof.
 10. The device of claim 9, wherein the cuttingtool comprises a ring having an inner region defined at the distal endof the elongate member, wherein the ribbon wire passes through the innerregion of the ring, and wherein the cutting blade is defined by acutting surface about an inner diameter of the ring.